Alkali anion exchange membranes are predominantly based on quaternary ammonium groups pendant to a polymer main chain (or “backbone”). The stability of quaternary ammonium groups is often poor in highly alkaline solutions and thus, the performance of these materials has been shown to rapidly degrade over time. There is a need to discover and explore positively charged polymers that offer the potential of improving alkali-stability.
Despite the wealth of literature on positively charged benzimidazolium species (including an abundance of literature on ionic liquids), polybenzimidazolium analogs remain relatively unexplored for ion-exchange materials. Notably, it has been reported that anion exchange materials can indeed be obtained by methylation of poly(benzimidazole) (PBI) and the resulting iodide ion exchanged for an anion of choice. However, the hydroxide form of this polymer is unstable. Therefore, a viable ion-exchange material formed from benzimidazolium or analogous materials has not yet been developed.